Prestretch fixture and combination thereof with drawing die press



R. A. MACKENZlE PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRESS April 18, 1967 8 Sheets-Sheet 1 Filed Aug. 12, 1966 j INVENTOR.

flOBE/QT A. MAZ'KE/VZ/E ATTORNEY.

BY l

April 1967 R. A. MACKENZIE 9 PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRESS Filed Aug. 12, 1966 s Sheets-Shet 2 F2 INVENTOR 05527 ,4. MAc/m/z/g ATTORNEY.

April 18, 1967 R MACKENZE 3,314,269

PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRESS Filed Aug. 12, 1966 8 Sheets-Sheet 5 INVENTOR.

ROBE/27 A. MA CKENZ/E/ @ATTORNEY.

P 18, 1967 R. A. MACKENZIE PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRF'sS 8 Sheets-Sheet 4 Filed Aug. 12, 1966 INVENTOR.

E a Z 1 N N R WM m c T A A M A W Fig/j 18, 1967 R. A. MACKENZIE 3,314,269

PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRESS Filed Aug. 12, 1966 8 Sheets-Sheet 5 i INVENTOR.

1 Boas/2r A. MA CKENZ/E Q9 7 I I f ATTORNEY.

April 13, 1967 R A. MACKENZIE 3,314,269

PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRESS Filed Aug. 12, 1966 8 Sheets-Sheet 6 I I 96 m 90 r 111 97 ATTORNEY.

April 18, 1967 R. A. MMMMMMM lE 3,314,269 I PRESTRETCH FIXTURE AND COMBINATION I M A Z [0 INVENTOR.

085??? ,4. MACKENZIE" BY W TTOENEY April 18, 1967 R. A. MACKENZIE 3,314,269

PRESTRETCH FIXTURE AND COMBINATION THEREOF WI'TH DRAWING DIE PRESS 8 SheetsSheet 8 Filed Aug. 12, 1966 BYZWI ATTORNEY United States Patent 3,314,269 PRESTRETCH FIXTURE AND COMBINATION THEREOF WITH DRAWING DIE PRESS Robert A. Mackenzie, Chagrin Falls, Ohio, assignor to The Cyril Bath Company, Cleveland, Ohio, a corporation of Ohio Filed Aug. 12, 1966, Ser. No. 575,487 20 Claims. (Cl. 72296) This application is a continuation-in-part of my copending application Ser. No. 514,219, filed Dec. 16, 1965, and entitled, Prestretch Fixture and Combination Thereof With Drawing Die Press.

This invention relates to a new and improved prestretch fixture and combination thereof with a drawing die press, and is an improvement on the invention disclosed in United States Patent of Cyril 1. Bath, No. 3,116,780, issued Ian. 7, 1964.

In accordance with the above patent, two prestretch units are arranged on the bed of an upright drawing press at opposite sides of the die space for tensioning sheet metal in one dimension into a range above its elastic limit preparatory to drawing of the sheet by cooperation of a pair of companion drawing dies.

Each unit comprises a gripping head which is connectable to the margin of the stock adjacent to it and is yieldably urged away from the die space by a hydraulic piston and cylinder assemblage. During the die closure, the gripping heads are pulled toward the dies against the yieldable hydraulic pressure by the metal sheet itself as the sheet is drawn by the dies endwise of the tensioning dimension, into the die cavity. Concurrently with their movement toward the dies, the heads are moved so as to wrap the stock about the forming face of the male die.

To permit these movements of the heads, each head is mounted on a carriage movable in slideways extending parallel to the tensioning dimension, and the slideways for the carriages are arranged on an elevator which moves upwardly and downwardly generally parallel to the path of the arm of the press. During the forming cycle, the heads are constrained to movement parallel to their starting or loading positions.

In the above structure the heads are operable independently of each other so that articles, such as automobile hoods, rear compartment covers, and the like, which are non-symmetrical with respect to a median line extending transversely of the tensioning dimension, can be formed readily. The machine of the above patent is one having general application and is satisfactory even for relatively high speed production. However, extremely high speed large quantity of production of a given shape is often desired, particularly by automobile manufacturers.

The present invention is directed to a structure whereby high speed quantity production of a sealed shape can be obtained effectively by mechanically applying positive forces, as distinguished from yieldable forces, to the heads for tensioning the sheet in one dimension while mechanically constraining the heads to follow exact paths properly preselected in relation to the dies and shape to be produced.

More specifically, a preferred embodiment of the invention is one wherein, instead of employing hydraulic pressure for applying yieldable tensioning forces to move the heads relatively apart and for permitting them to be drawn toward the dies by the sheet being tensioned and formed, the heads are moved downwardly by forces directed parallel to the ram path, and are diverted laterally of the ram path and caused to move away from and toward the dies by components of force imposed by the reactions of the downward forces and suitable rigid links of fixed length.

Each link, at one end, is pivotally connected to an 3,314,269 Patented Apr. 18, 1967 associated one of the heads, by way of the horizontally movable carriage on which the head is fixedly mounted, and at the other end is mounted on a pivot which has an axis in fixed position relative to the one of the drawing dies which is mounted on the bed of the press. The axes of all of these pivotal connections are parallel and extend transversely of the tensioning dimension.

In order to constrain the heads to travel in the proper paths, the pivots which are in fixed position relative to the die on the bed are positioned in unsymmetrical relation to a median line of the forming face of the die which extends transversely of the tensioning dimension, or parallel to the pivotal axes. The links, when so used with the non-symmetrical arrangement of the pivotal axes, may be of the same length or of different lengths. In some few cases the pivotal'axes of the pivots which are fixed relative to the die on the bed may be symmetrically arranged relative to the median line, in which case the links must be of different lengths from each other.

Preferably these pivots of the links which are in fixed position relative to the die are mounted directly on the die itself so that the die with the proper links mounted in proper position can be removed readily as a unit from the press and reinstalled readily when desired, thus greatly reducing the removal and set-up time in case the press is to be used temporarily for making other parts. If desired, the gripping heads may be left attached to the pivots and thereby included as part of the unit thus removed.

Again, since it may be desirable to use the press for general production, the stretch forming piston and cylinder assemblages, such as disclosed in the above identified patent, may be left intact on the elevators of the stretch unit, and the opposite ends of the cylinders vented to a suitable sump, directly if their function is to be completely eliminated, and through throttling valves if they are to function as shock absorbers for reducing the shock imposed on the elevators and carriages of the heads during forming.

The present invention has particular advantages in that, during die enclosure, the heads can approach the associated marginal limits of the dies in such manner and to such a degree that the gripped margin of the stock can be brought substantially to the associated limits of the die forming faces. As a result, substantially all of the sheet stock except those marginal portions actually being gripped between complementary gripping jaws of the heads can be made accessible for drawing by the dies while the sheet is held under tension by the heads, thus reducing scrap to a minimum and effecting very large savings in stock material.

For purposes of illustration, the present invention is described hereinafter in connection with the forming of metal stock between the matching male and female drawing dies in an upright press wherein the ram travels vertically, the male die is positioned with its length extending in the tensioning dimension, and the units are positioned at opposite ends of the die. It will be apparent that these positions and directions in the description and claims are not absolutes, but are for convenience in describing the relative positions and movements on the parts of the structure.

Furthermore, While in most cases it is desirable that two movable stretch heads be employed, there are instances in which the stock can be held in fixed position at one end and only one stretch head moved for stretching the stock and laying it onto the male die.

Specific advantages of the present invention reside in the precise maintenance of the overall size of the formed sheet so that it fits accurately in the subsequent trim dies, in the elimination of a large amount of expensive hydraulic equipment, in the positive and accurate movement of the heads at high speed, in relieving of the sheet stock from the necessity of pulling the heads toward each other as the sheet stock is drawn into the die cavity, in the reduction in setup and removal time when changing from production of one shape to another, and in the large reduction in scrap.

Various other objects and advantages of the invention will become apparent from the following description of the drawings, wherein FIG. 1 is a front elevation of a drawing die press incorporating the stretching units of the present invention;

FIG. 2 is a top plan view of one of the stretch units of FIG. 1;

FIG. 3 is a front elevation of the unit illustrated in FIG. 2;

FIG. 4 is a vertical sectional view of the unit illustrated in FIG. 2, and is taken on line 4-4 thereof;

FIG. 5 is an enlarged fragmentary left side elevation of the unit illustrated in FIGS. 2 and 3;

FIGS. 6, 7 and 8 are diagrammatic illustrations, respectively, of the draw dies and units of the present invention, showing relative positions of the heads and dies during the sheet loading, wrapping, and final forming operations, respectively;

FIG. 9 is a diagrammatic illustration showing hydraulic circuitry of one of the units and of the press ram;

FIG. 10 is a figure similar to FIG. 1, but showing a mechanical press and mechanical driving of the stretch heads by the ram thereof;

FIG. 11 is a diagrammatic fragmentary front elevation of a mechanically driven press and a modified push rod interconnecting the ram and stretch head elevator;

FIG. 12 is a diagrammatic illustration showing one procedure facilitating the locating of the axes of the pivots for the links; and

FIG. 13 is a fragmentary view illustrating a modified form of link means for the stretch heads.

Since both units may be the same in form and function, )nly one unit and its hydraulic circuitry will be described n detail.

Referring to the drawings, the invention is shown in- :orporated in a conventional upright hydraulic press 1 raving a bed 2 with upright guide members 3 arranged it the corners and guiding a ram 4 for vertical reciprocaion. The bed supports a male drawing die 5 which as a forming face which is convex upwardly, both trans- 'ersely and lengthwise. The ram supports a complenentary female drawing die 6. The dies 5 and 6 define, when closed, a concave-convex pattern or patterns into vhich the sheet metal is drawn by the dies. The stock s tensioned by the stretch units along one dimension only, nd conventional hold down rings or devices are not emloyed.

Since the present invention is particularly adapted for arming articles which are non-symmetrical about a medin line extending transversely of the tensioning dimension, 1e dies 5 and 6 are shown as designed for forming such rticles.

The ram is driven on its forming and return strokes y means of hydraulic piston and cylinder assemblages including cylinders 8 and pistons 9 having piston rods ll secured to the ram.

Stretch units are mounted on the bed 2 adjacent those [argins of the die which are opposite from each other i the tensioning dimension which margins, for brevity l description, are referred to hereinafter as the end argins even though the tensioning dimension is the iorter dimension of the sheet.

As more fully described in the above patent, and illusated in FIGS. 2 through 5, each unit comprises a base ate 13 on the front and rear of which are mounted guide .pports 14 which support upright guides 15. Each ride 15 has upright slide surfaces 16 facing inwardly the unit in a direction forwardly and rearwardly of e bed, and upright guide faces 17 at right angles to e surfaces 16. Mounted for vertical reciprocation in the slideways is a stretch head elevator 20 which is guided thereby for movement upwardly and downwardly while the elevator itself remains parallel to its starting position.

For moving the elevator 20 upwardly and downwardly, suitable piston and cylinder assemblages 2-1 are provided, one at each end of the elevator. Each assemblage comprises a cylinder 22 mounted in fixed position on the elevator. A piston 23, having a piston rod 24, is reciprocable in the cylinder. The cylinder 22 is arranged so that the piston rod extends downwardly and at its lower end carries a tongue 25 by which it is pivotally connected by a horizontal pivot 26 to a suitable yoke 27 which is fixedly secured to the base 1 3 of the associated unit. Thus, upon introduction of the hydraulic pressure fluid to the rod ends of the cylinder 22, they move the elevator downwardly, and by introduction of the fluid to the head end of the cylinders, they move the elevator 20 upwardly. These movements are under yieldable hydraulic pressure and are controllable independently of the operation and control of the ram piston and cylinder assemblages 7. The elevators are also controllable independently of each other. Thus the elevators can be raised and lowered independently of each other and of the ram in preselected variable relation with respect to the rise and fall of the ram.

If desired, instead of the assemblages 21, the elevators may be moved upwardly and downwardly by push rods connected thereto and to the ram, as disclosed in U.S. Patent No. 3,113,607 of Paul Maize, issued Dec. 10, 1963, or in the co-pending application of Stanley M. Dolney, Serial No. 517,616, filed Dec. 30, 1965, and entitled, Hydraulic Push Rod for Stretch Draw Press, as referred to hereinafter in connection with FIG. 10.

In order to tension and stretch the stock independently of the stretching. caused by die closure, suitable stretch heads 30 are provided, one for each unit 11. Each head comprises an elongated body 31 which, lengthwise, extends forwardly and rearwardly of the press bed and thus transversely of the dimension in which the stock is to be tensioned. Each head has complementary gripping jaws 32 and 32:: which are opened and closed by links 33 and 34, operated by piston and cylinder assemblages. The assemblages comprise cylinders 36 in which are pistons 37 having piston rods 38. The rods 38 are connected to the body 31 by pivots 39 and the cylinders are pivotally connected to the links 33 and 34.

As hereinbefore mentioned, it is desirable that each stretch head move at all times parallel to its loading or starting position wherein its inner or loading face, which is the face through which the jaws open for receiving the margin of a sheet of metal to be stretched and formed, is generally upright and facing toward the ends of the dies. This permits the portion of the sheet between the heads to be subjected to the dies substantially to the inner faces of the heads, thus utilizing all the metal which is not actually being gripped by the jaws themselves.

In order to constrain each head to movement parallel to its original position, each carriage 50, on which an associated head is fixedly mounted, is connected by pivots *53 to the upper ends of upwardly extending links 54. The lower ends of the links are connected by pivots 55 to the elevator 20. In order to prevent the heads swinging downwardly about the axes of the pivots 53, the elevator 20 is provided with upwardly facing horizontal tracks 56 near the outer edges and midportion of the carriage 50, and suitable rollers 57 are provided on the carriage, for rolling along the tracks 56. In addition, to prevent swinging of the head upwardly about the axis of the pivot 53, the elevator 20 is provided at each end of the head with hold down rollers 58 which engage upwardly facing horizontal trac'kways 59 on the end portions of the head.

These connections and rollers constrain the head 30 to move relatively to the elevator 26 in horizontal paths at all times, and thus parallel to their starting or loading positions.

The position of the stretch head illustrated in FIG. 4 is the innermost position in which the rollers 57 are closely adjacent the inner edge of the elevator which is the edge adjacent to dies. In this position the link 54 is in a rotated position slightly past the vertical in a direction toward the dies.

In order to move the heads toward and away from the dies as they are raised and lowered, the heads are connected to suitable links which swing about pivots which are fixed in relation to the male die on the bed. As illustrated in FIGS. 6 through 8, one of the heads 30 is connected to one end of a set of links60 by means of coaxial pivots 61 so that the head can rock relative to its associated links. The links are rigid and of fixed length, and generally two links are provided for each head, one at the front of the head and one at the rear. They function as a single rigid link.

The other ends of these links are mounted on coaxial pivots 62 for swinging about a common axis thereof. The pivots 62 are mounted in fixed position relative to the die 5, and their common axis extends horizontally, transversely of the tensioning dimension, and is below the level of the upwardly facing convex forming face of the die 5.

In the form illustrated, the pivots 62 are mounted directly on the die so that the die, the associated carriage, the associated links, and associated head can be removed as a unit from the press for storage and reinstalled as a unit.

correspondingly, the other head 30 is connected, by Way of its carriage St), to one end of a pair of links 63 by coaxial pivots 64 so that the head can rock relative to its links 63. The other ends of the links 63 are connected to coaxial pivots 65 which are parallel to the pivots 62 and are in fixed position relative to the die 5, preferably directly on the die so that these links, pivots, head and carriage can also be removed as a unit with the die.

The forming face of the die is unsymmetrical relative to a median line in an upright median plane y-y which is midway between the ends of the die face, as indicated in FIG. 6, and extending transversely of the tensioning dimension. The set of pivots 62 and set of pivots 65 are unsymmetrically arranged relative to this median line. Generally the links 60 are of different lengths than the links 63 depending upon the shape of the forming face of the die.

In the few instances wherein the links 69 and 63 are of the same length, the sets of pivots 62 and 65 must be thus nonsymrnetrically arranged. In all cases, each head is constrained to move in a path different from, and unsymmetrical relative to, the path of the other head.

With the sets of pivots 62 and 65 unsymmetrical arranged with respect to the median line in the plane y-y, the links 60 and 63 in some cases may be of the same length, though generally they are of dilferent lengths from each other, as above mentioned. In any case, if the sets of pivots 62 and 65 are not unsymmetrically arranged relative to the median line in the plane yy, then the links 60 necessarily must be of different length than the links 63. The positions of the pivots and their associated links are such that upon initial downward movement of the heads the links cause the heads to move relatively apart from each other with non-yielding force to tension the stock to the desired range. When the heads continue downwardly, they may continue to be moved farther apart by the links, at least during a part of their stroke. Usually as they are moved toward the lower portion of their downward path, they cease moving apart and are moved back inwardly toward the die 5 by the links so that their inner or loading faces become positioned finally substantially at the lower edges, respectively, of the ends of the forming face of the die 5 Each head remains always during this travel a fixed distance from the axis of the associated pivot on the die 5. Accordingly, the inward movement of each head requires swinging of the axes of the pivotal connections of the links with the heads inwardly toward the dies.

In some cases, the movement of one head may be outwardly throughout its 'entire downward travel, and that of the other head may be partly outwardly and then back inwardly toward the dies. These movements can readily be predetermined from the particular article to be made, and the pivot positions and lengths of links adjusted accordingly. The links are adjustable in length for convenience in selecting the optimum length for a particular shape. Once adjusted, they usually are welded so as to retain the adjusted length.

Preferably, in all cases, the heads are arranged so that they move relatively apart to tension the stock somewhat to take out the ordinary sag and waviness without causing the tension to reach the elastic limit before the sheet engages the highest peak or portion of the forming face. This tension generally is maintained until the stock is engaged with the peak, or for a very limited distance therebeyond toward the gripped margins of the sheet. Separation of the heads continues as they lower. By the time the stock has engaged the peak and adjacent areas of the die as above described, the sheet stock is tensioned into a range above the elastic limit. This tension is maintained as the sheet is wrapped about the forming face of the male die, and may be maintained throughout the drawing of the sheet by the dies. If desired, the sheet may be tensioned above the elastic limit before contacting the forming face of the die 5. In either event, the stock is tensioned above its elastic limit before its formation by the cooperation of the dies.

In some instances, the inward movement of the heads may be such that the tension applied by the heads is reduced as the stretching forces imposed by the die closing increase, so as not to overstress the metal.

It must be remembered that the action of the present structure is very rapid, and hence the time which elapses between partial and full closure of the dies often may be such that though the tension that was being applied by the head to tension the stock above the elastic limit is reduced before full closure below that required to tension above the elastic limit, the sheet retains its more readily flowable condition until the dies are fully closed.

Having reached this elastic limit and been pulled downwardly around the male dies, the heads are controlled so that their inner faces are closely adjacent to or substantially at, their associated ends of the dies, respectively, upon final closure of the dies. Thus, the only waste in trim of the stock in the tensioning dimension is that stock which is actually between the gripping jaws of the heads, or in some cases, a small fraction of an inch inwardly toward the dies therefrom.

It is apparent that with this arrangement the die with its associated links and pivots, and gripping heads also if desired, may be removed as a unit, or the linkages and dies removed as a unit, with assurance of proper cooperation of the heads and dies upon replacement of a die within the press.

As hereinbefore mentioned, the usual hydraulic piston and cylinder assemblages for tensioning stock may be eliminated. In general, this is the case. There are, however, a few instances in which it may be desired to retain them.

If they are so retained, they may be such as disclosed in the above patent to Cyril I. Bath, No. 3,116,780. As therein more fully described, they include a plurality of piston and cylinder assemblages, indicated generally at 72, arranged in double banks 73, .each bank 73 comprising a single rigid body 74 having radially spaced parallel cylinders 75 therein provided with liners 76. The body 74 is provided with trunnions 77 rockably supported in 7 suitable uprights 78 and 79 which are rigid With the elevator 20.

Each cylinder 75 carries a piston 80 with a piston rod 81 which is pivotally connected by pivots 83 to associated rocking link 54.

The position of the stretch head illustrated in FIG 3 and 4 is the innermost position in which the rollers 57 are closely adjacent that edge of the elevator adjacent the dies. When in this position, the links 54 are in a rotated position slightly past the vertical in a direction toward the dies. When they are in this position, the pistons 80 are in their most nearly retracted position. Upon introduction of pressure fluid the head ends of the cylinders 75, the pistons it} are thrust to the right in FIG. 4, thereby swinging the links 54 counterclockwise about the pivots 55. During this swinging movement, the axes of the pivots 83 rise slightly above the horizontal until the links 54 are upright, and then lower again to a position at the same level as the pivot had in the starting position. Since the trunnions 87 support the cylinders 75 for rocking about a horizontal axis, this component of vertical movement of the pivots 83 is compensated without causing any binding stresses.

When pressure fluid is supplied to the head ends of the cylinders 75, it urges the pistons 80 to the right in FIG. 4, thus causing the links 54 to swing clockwise about the axes of the pivots 55, and thereby pull the carriage 59 to the right.

In the operation of the fixture, both units may be operated concurrently, or one may be hydraulically looked so the stock is stretched from one only while anchored in fixed position relative to the dies in a direction endwise of the ram, or the cylinders of one or both units may be vented, as hereinabove described.

Each head can be raised and lowered by means of its elevator independently of the other, as each has its Own separate and independent hydraulic circuit.

For purposes of illustration, the units and ram are shown as controlled manually by remote control valves and circuitry, as illustrated in FIG. 9. As therein shown, the pressure for fluid for the operation of the ram is supplied by a suitable pump 99 driven by a motor 91 having its pressure side connected to assemblages 7 by a line 92 through a remotely settable pressure control regulator 93 and solenoid operated valve 94. The valve 94 can hydraulically lock the assemblages 7, or supply pressure to the head ends of both concurrently for forcing the ram downwardly while venting the rod ends. The valve 94 may be set to reverse the flow of hydraulic fluid for lifting the ram.

Since the circuitry for operating each stretch forming .lnit is separate and distinct from that of the other, each iaving its own complete circuit and fluid pressure source, )nly one will be described for purposes of illustration. Each unit is supplied with hydraulic pressure fluid from 1 pump 96 driven by a motor 97. The pressure is sup- )lied to the opposite ends of the elevator assemblages 21 hrough a suitable solenoid operating control valve 98 vhich can hydraulically lock. the assemblages 21 or admit tressure fluid to one end and vent the other end concurently to sump.

The pump 96 is also connected through a suitable conrol valve 99, which supplies the pressure fluid to the cyliders 75 of the hydraulic stretch forming piston and ylinder assemblages described. This valve is arranged that the flow of hydraulic fluid to the opposite ends of 1e assemblages can be reversed, the ends opposite the ressure ends being connected to sump. When the valve 9 is in an intermediate position, the cylinders 75 can be ydraulically locked so that the associated unit can funcon merely as an anchorage and all the stretching can e performed by the opposite unit. The pump 96 also suplies pressure fluid through the solenoid operated valve 91 to the gripper jaw operating assemblages. The preslre and flow of the fluid delivered to the piston and cyltder assemblages may be regulated by any conventional remotely controlled hydraulic pressure and flow regulators. For example, a settable pressure regulator 102 which may be remotely controlled by a driving motor 103, may be provided between the valve 99 and the pressure side of the pump 96. A similar regulator 104 operated by a remotely controlled motor H35 may be interposed between the pressure side of the pump 96 and the valve 101. A like pressure regulator 196 remotely controlled by a motor 197 and a flow regulator 168 controlled by a motor 199 may be interposed between the pump 96 and the valve 98.

If it is desired to render the assemblages inoperative, its ends may be disconnected from the valve 99 and the cylinders drained.

If, however, the assemblages are to be used as shock absorbers, their ends may be connected to valves 119, each of which can be set, selectively, in one position wherein it connects its associated end of the cylinder to the valve 99 and in another position wherein it connects its associated end of the cylinder to an adjustable throttling orifice 111.

As hereinbefore mentioned, it may be desirable in some cases to move the elevators, and thereby the heads, downwardly by push rods connected to the ram, as in the above identified patent No. 3,113,607, to Paul F. Maize, or the copending application, Serial No. 517,616, filed December 30, 1965, of Stanley M. Dolney. Such a structure is illustrated generally in FIG. 10 herein, wherein is shown an upright mechanical press 112 having a ram 113 driven by a suitable flywheel and clutch arrangement 114.

In this form of the invention, two stretch units 115 such as hereinbefore described, are arranged at opposite sides of the die space. However, instead of moving the vertically movable elevators of these units downwardly by piston and cylinder assemblages, they are moved by push rods on the ram. As illustrated, each elevator 116 is en gaged by four push rods 117, arranged one pair at each of its ends. These push rods may be adjustable in length, as described in the Maize patent, or may be of the shock absorbing type, as described in the Dolney application.

Each push rod is connected to the ram for movement downwardly therewith. The rods for one stretch unit may be adjusted to a different length than for the rods of the other unit so that the rods of one unit engage its elevator and start its movement downwardly before the rods of the other unit engage their associated elevator and start it downwardly. Thus a stretch head of one unit may move downwardly a different distance and in different timed relation to the other unit.

In all of the forms illustrated, the inward and outward movement of the heads is effected by the links, such as the links 60 and 63.

As mentioned above, the push rods may be such as described in the above Maize patent or may be a modified form such as disclosed in the above co-pending application of Stanley M. Dolney, and as diagrammatically illustrated in FIG. 11 hereof.

Referring to FIG. 11, a mechanical press is employed. A male die 120 is carried on the press bed. A mechanically driven ram 121 carries a complementary female die 122. The stretch heads 123 are mounted on elevators 124 which are movable vertically in suitable frames 125. Each elevator frame has the usual downwardly extending rigid plate portion 126 which bottoms out on the bottom of the frame when the elevator is in its lowest possible position. The distance which the elevator can be moved downwardly from its raised or starting position may be reduced so that there is a dwell of the head at the desired lowered position. For this purpose, suitable rigid blocks 127 are placed on the base of the elevator frame and in position to be engaged by the downwardly extending portion 126 of the elevator.

For lowering the elevator, telescopic hydraulic push rods 128 are employed, disposed as in the Maize patent. In the form illustrated, each rod 128 comprises a cylinder 129 secured in upright position on the ram and a piston 130 reciprocable therein. The piston has a piston rod 131 which is connected to the top of the elevator 124. The head end of the cylinder 129 is connected to a settable relief valve 132. The valve 132 is such that when the downward pressure applied by the ram to the elevator exceeds a preselected amount adequate to operate the elevator, the valve permits the escape of pressure fluid from the head end of the cylinder to a sump S. A check valve 133 is interposed between the head end of the cylinder and the sump S and opens to permit the drawing of fluid into the head end of the cylinder from the sump and closes to prevent its return through the check valve, and to cause the fiuid to flow through the settable relief valve.

With this arrangement, as more fully described in the above identified application of Dolney, before the female die has come in contact with the sheet stock, the elevators have been forced down by the arm for wrapping the stock about the ram die 12%, the necessary tension on the sheet being effected by links 134 such as hereinbefore described. When the elevator has moved downwardly to the required position so that the gripped margin of the stock is substantially at the lower edge of the male die forming face, the downward projection 126 engages the selected blocks 127 and prevents further downward movement of the elevator and head. As the ram continues to descend, however, the pressure in the cylinder 129 builds up to a point beyond that necessary to lower the elevator and this excess pressure is vented through the valve 132 as the ram descends to its lowermost position and causes the female die 122 to draw the sheet into conformance with the drawing face of the male die 120.

The elevator may be returned upwardly to its starting position by conventional return means such as described in the above Maize patent, but in any event, if not returned as soon as the ram has lifted so that the piston is in the bottom of the cylinder 129, the cylinder acts to lift the piston and its rod and thereby the elevator to starting position. The push rod for one unit are effective entirely independently of those for the other so that one elevator can stop independently of the other, and also can start independently of the other depending upon the lengths of the associated push rods. In the latter case, the rod for one unit may be such as to lift free of the elevator after the elevator has reached its upward position.

If desired, the power applying means for lowering the elevators may be applied to the links but it is preferable that they be applied directly to the elevators.

In those cases in which complete mechanical operation is desired, except for the small hydraulic system necessary to open and close the gripping jaws, it is most convenient to derive all force for lowering the elevators directly from the ram as described in connection with FIG. 10. This force from the ram and the resultant forces derived from the combination thereof with the reactionary forces imposed by the links, are used to divert the heads laterally of the ram path and cause them to move toward and away from the dies as required by the particular shape being formed. This is particularly desirable because, near the end of the forming operation, the force of the mechanical ram is at its maximum and is more than adequate to effect closure of the dies down- Ward movement of the elevators, and inward and outward movement of the heads.

Referring to FIG. 12, the male die and one manner of facilitating locating the pivotal axes, such as the pivotal axis 65, is illustrated. A point a representing the edge of the gripping jaws nearest to the die 5 is located in a horizontal plane xx which is about one inch below the crest of the male die, the point a being disposed outwardly endwise of the die in the tensioning direction at the position such edge is to have when the sheet has had its initial preselected stretch into a range above the elastic limit. A point b at which the jaw edge is to be located at the end of the wrapping and forming operation is selected. The location of point a is based on the preselected elongation to be given the particular sheet, and this, in turn, depends on the shape and type of metal. The location of point b is determined in accordance with the predetermined position the jaw edge is to assume having due regard to conservation of stock, allowance for handling and trimming operations, and the die shape.

The points a and b are connected by a line c which is then bisected by a right angle bisector d. The line 0 is assumed to be the chord of a circle of which the center is on the line d. Thus, generally, the axis 65 will be at a selected location along the line d. The location along line d is selected in accordance with the circular path to be followed by the head.

The length of the link 63 will be chosen so that the edge of the jaws nearest the die will follow, as near as practical, a path from a point e, somewhat inwardly and above point a, at which the head grips the untensioned sheet and then passes along the circular path through points a and b.

In FIG. 13 there is illustrated a die which may be similar to the die 5. Instead of providing links, such as the set of links 69, or the set of links 63, with one link at the front and one at the rear of each head, a single central link is provided for each head.

In such case, the heads 136 and 137 are arranged at opposite ends of the die as heretofore. A rigid link 138, of generally C-shape structure, is pivotally connected at the end of one of its arms by a pivot 139 to the die and at the end of its other arm by a pivot 14!? to the head 136. The link 138 is of sufiicient rigidity to withstand the entire tensioning strain that may be imposed on the head 136.

Correspondingly, a link 141 of C-shape is connected by a pivot 142 to the die 135 and by a pivot 143 to the head 137. Thus, the link 138 provides a link means which is, in operating effect, the equivalent of the link means provided by the set of links 60, and the link 141 provides a link means corresponding to the links 63.

Having thus described my invention, I claim:

1. A die and stretch head combination comprising: a die having a forward forming face which is convex forwardly and is unsymmetrical in section in a first plane extending in the direction of one of the dimensions of the face and intersecting the face; stretch heads located adjacent those limits of the forming face which are opposite from each other in said direction and adapted to grip two opposite margins, respectively, of a sheet of metal stock;

first and second pivot means having axes, respectively,

which extend transversely of said dimension, are in fixed position relative to the die face, and are arranged unsymmetrically relative to, and at opposite sides of, a reference plane which is at a right angle to the first reference plane and which includes that median line of said face which extends transversely of said dimension;

first and second link means, each of fixed length, supported by the first and second pivot means, respectively, each for swinging about the axis of its associated pivot means;

means connecting the stretch heads to the link means,

respectively, each head for swinging with its associated link means toward and away from the die, and constraining the heads each to a fixed distance from the axis of the pivot means of its associated link means during swinging of its associated link means. 1

2. The structure according to claim 1 wherein the constraining means are arranged relative to the die and head so as to constrain the head, during swinging movement of the link means from starting to final forming position, to positions which are substantially parallel to the starting position of the head.

3. A structure according to claim 1 wherein the constraining means comprise a carriage member and an elevator member, one of the members being supported on the other member for movement along a predetermined fixed path relative to the other member, and means support the other member for movement independently of the movement of said one member in a fixed path at substantially right angles to said predetermined fixed path, and said one of said members is connected to the head. 4. The structure according to claim 1 wherein power means are provided for the heads, respectively, for swinging the heads downwardly independently of each other. 5. A structure according to claim 1 wherein the first link means is of different length than the second link means.

6. A die and stretch head combination according to claim 1 wherein said first and second pivot means are connected directly to the die with their axes in parallel relation to each other.

7. The structure according to claim 1 wherein the pivotal axes of the first and second pivot means are parallel to each other and are spaced from the forming face, and the axis of the first pivot means is spaced from said forming [face a greater distance than is the axis of said second pivot means.

8. A structure according to claim 1 wherein the axes of the pivot means are spaced from the forming face in a position such that the heads can move from a position generally forwardly from the face to a position generally rearwardly from the face.

9. A die and stretch head combination according to claim 8 wherein the axes of said pivot means are sufficiently close to the forming face so that the link means can be swung to a forward position wherein the heads are in a position for supporting a length of sheet stock therebetween in forwardly spaced relation from the convex side of the forming face, and the link means can be swung rearwardly relatively away from each other from said forward position to a position wherein the gripped margins of the sheet are at least as far rearwardly as the rearward limits of the adjacent margins of the forming face, respectively.

10. The structure according to claim 9 wherein the length of at least one of the link means and the location of the axis of its associated one of the pivot means are such that the associated head, in swinging rearwardly from a position forwardly of the die face, moves first away from the midportion of the die face in the direction of said tensioning dimension and, upon continued swinging rearwardly, moves in the opposite direction.

11. A die and stretch head combination comprising: a die having a forward forming face which is convex forwardly and unsymmetrical in section in a first reference plane extending in the direction of one of the dimensions of the face and intersecting the face;

stretch heads located adjacent those limits of the forming face which are opposite from each other in said direction;

first and second pivot means having axes, respectively,

which extend transversely of said dimension and are in fixed positions, respectively, relative to the die face;

first and second link means, each of fixed length, supported by the first and second pivot means, respectively, each link means for swinging about the axis of its associated pivot means, from a starting position to a position rearwardly of said face;

gripping heads connected to the link means, respectively, each. for swinging with its associated link means;

each head being constrained to a fixed distance from the axis of the pivot means of its associated link means;

characterized in that the first link means is of different length than the second link means, and in that, in the rearmost position of the link means, relative to said face the heads are positioned closely adjacent to the ends of said face.

12. The structure according to claim 1 wherein the constraining means are connected to the head and positively constrain the head, at least during movement as the link means approach said final position, to predetermined rocked positions relative to the link means about the axis of the second pivot means independently of the direction of reactionary forces that could be imposed on the head by stock being tensioned by the head.

13. The structure according to claim 11 wherein the axis of the first pivot means is spaced from the forming face a greater distance than is the axis of the second pivot means.

1 The structure according to claim 13 wherein the axes of the first and second pivot means are arranged nnsymmetrically at opposite sides of a reference plane intersecting the face and at right angles to the first reference plane, and incorporating that median line of the face which extends transversely of the tensioning dimension.

15. A stretch draw press comprising:

a bed member,

a power driven ram member movable toward and away from the bed member,

one of said members having a first die supporting area adapted to support a male drawing die in fixed position relative thereto, the other of said members having a complementary die supporting area aligned with the first supporting area and adapted to support a companion drawing die in fixed relation thereto,

a pair of gripping heads spaced apart from each other endwise of said first area and adapted for gripping two opposite margins of a length of sheet stock for applying tension thereto in one dimension when the heads are moved relatively apart from each other endwise of said first area,

first and second pivot means parallel to, and spaced from, each other and having axes, respectively, which extend transversely of said first supporting area and which are in fixed relation to said one member, and thereby in fixed relation to a male die when a male die is supported on said one member,

first and second rigid link means supported by the first and second pivot means, respectively, each for swinging about the axis of its associated pivot means,

means connecting said gripping heads to the link means, respectively, and constraining the heads to swing in arcuate paths, respectively, each at a fixed distance from the axis of the pivot means of its associated link means, during swinging of its associated link means,

said pivot means and link means being so arranged that said paths of the heads diverge at least along their initial portion in a direction of movement of the heads from starting position towards said one member, and

power means for moving the heads along their respective arcuate paths while the heads are so constrained.

16. A structure according to claim 15 wherein the power means are push rods operatively connected to said other member and to the heads.

17. A structure according to claim 15 wherein a male drawing die is supported in fixed position on said one member,

a companion drawing die is supported in fixed position on the other member,

said male die has a convex forming face which is generally convex toward said companion die, and

control means for the power means are provided and arranged to cause the power means to move the heads along said fixed arcuate paths in a relation to the movement of the dies relatively toward each other such that the heads wrap the stock on the male die before the female die comes into final contact with the stock.

18. A structure according to claim 17 wherein the heads have inner loading faces from which, when loaded for stretching, the gripped sheet metal stock protrudes edgewise, and

constraining means are mounted on said one member and are connected to the heads, respectively, and positively constrain the heads, at least during movement of the heads as the link means approach their final positions, respectively, to positions in which said faces face toward, and in the final position are very close to, their associated adjacent limits of the forming face die.

19. The method of forming sheet metal stock unidimensionally into conformance with a male die having a forming face of which at least one portion is convex forwardly and forms a forwardmost crest area extending transversely of the tensioning dimension, and comprising,

(a) first gripping two opposite margins of the stock and thereby holding the stock in face to face spaced relation to said crest area,

(b) then, before the sheet is stretched, moving the sheet flatwise toward said face until the sheet is in firm engagement with said crest area, and

(c) by moving the margins in preselected invariable fixed paths, respectively, such that upon continuing said movement in said paths the stock is wrapped onto the remainder of the die face and is tensioned unidimensionally into a range above the elastic limit, and the tension is maintained above the elastic limit at least during said wrapping about the major portion of the remainder of the die face.

20. A die and stretch head combination comprising:

a die having a forwardly facing forming face which is convex forwardly and is unsymmetrical in section in a plane intersecting the face and extending in one dimension of the die,

stretch heads located adjacent opposite limits of said dimension of the die and adapted to grip opposite end margins of a sheet of metal for applying tensioning force thereto for stretching the sheet unidimensionally in said dimension,

first and second pivot means connected to the die and having axes, respectively, which extend transversely of said die, are in fixed position relative to the die face, and are so arranged that the axis of said first pivot means is spaced from the forming face a greater distance than is the axis of the second pivot means,

first and second link means supported by the first and second pivot means, respectively, each for swinging about the axis of its associated pivot means and each link means being of fixed length and of different length than the other link means, and

connecting means connecting the heads to the link means, respectively, each for swinging at a fixed distance from the pivotal axis of the pivot means of its associated link means, for applying said tensioning force to the stock in said dimension and for wrapping the stock on the die face.

References Cited by the Examiner UNITED STATES PATENTS 1,622,590 3/ 1927 Jolstad 72297 2,442,268 5/ 1948 Fields et al. 72297 2,762,417 9/1956 Oeckl 72297 2,825,385 3/1958 Allen 72296 3,116,780 1/1964 Bath 72297 CHARLES W. LANHAM, Primary Examiner.

R. D. GREFE, Assistant Examiner. 

1. A DIE AND STRETCH HEAD COMBINATION COMPRISING: A DIE HAVING A FORWARD FORMING FACE WHICH IS CONVEX FORWARDLY AND IS UNSYMMETRICAL IN SECTION IN A FIRST PLANE EXTENDING IN THE DIRECTION OF ONE OF THE DIMENSIONS OF THE FACE AND INTERSECTING THE FACE; STRETCH HEADS LOCATED ADJACENT THOSE LIMITS OF THE FORMING FACE WHICH ARE OPPOSITE FROM EACH OTHER IN SAID DIRECTION AND ADAPTED TO GRIP TWO OPPOSITE MARGINS, RESPECTIVELY, OF A SHEET OF METAL STOCK; FIRST AND SECOND PIVOT MEANS HAVING AXES, RESPECTIVELY, WHICH EXTEND TRANSVERSELY OF SAID DIMENSION, ARE IN FIXED POSITION RELATIVE TO THE DIE FACE, AND ARE ARRANGED UNSYMMETRICALLY RELATIVE TO, AND AT OPPOSITE SIDES OF, A REFERENCE PLANE WHICH IS AT A RIGHT ANGLE TO THE FIRST REFERENCE PLANE AND WHICH INCLUDES THAT MEDIAN LINE OF SAID FACE WHICH EXTENDS TRANSVERSELY OF SAID DIMENSION; FIRST AND SECOND LINK MEANS, EACH OF FIXED LENGTH, SUPPORTED BY THE FIRST AND SECOND PIVOT MEANS, RESPECTIVELY, EACH FOR SWINGING ABOUT THE AXIS OF ITS ASSOCIATED PIVOT MEANS; MEANS CONNECTING THE STRETCH HEADS TO THE LINK MEANS, RESPECTIVELY, EACH HEAD FOR SWINGING WITH ITS ASSOCIATED LINK MEANS TOWARD AND AWAY FROM THE DIE, AND CONSTRAINING THE HEADS EACH TO A FIXED DISTANCE FROM THE AXIS OF THE PIVOT MEANS OF ITS ASSOCIATED LINK MEANS DURING SWINGING OF ITS ASSOCIATED LINK MEANS. 